The present invention pertains to bridges, and more particularly to bridges which may be transported by road vehicles, and erected at the site.
Transportable bridges have been developed over the years, particularly in connection with the movement of armies during warfare. The need has increased, as the mobility of the armies has increased. Such needs, ever expanding, are for improved transportability, the ability to be easily and quickly erected, the ability to span over larger depressions, such as ravines and streams and rivers, and the ability to carry larger loads.
Among the developments in the arts of transportable bridges there may be mentioned a bridge comprising sections made of structural members, relatively elongate, and having a top, a bottom and a pair of connecting sides, so as to provide a somewhat tubular section of substantially square cross section. An abutment section was provided, somewhat in the nature of a semi-trailer, equipped near one end with a set of wheels, and near its other end with a coupling for attachment to the "fifth wheel" of a tractor vehicle. This first section served as an abutment and upon arrival at the site, jacks were lowered to support the section, the tractor was disconnected, and the wheels of the section were elevated. Additional sections were provided, which could be telescoped within the first mentioned section, and these were joined end to end, and pushed through the first or main supporting section. The secondary sections, connected end to end, upon being pushed through the main section, provided a substantial weight cantilevered outwardly and over the depression, being supported only by the first or main section. To counterbalance this weight, additional sections were added, so that there was substantially the same number of sections to counterbalance as there were sections extending over the depression. In that way, substantially twice as many sections were required as were needed to span the depression. In addition, such prior art bridge could not span very wide depressions, nor could it carry very great loads. When in place, it had no abutment, merely the provision of the end sections of the bridge resting upon the two banks of the depression.
In another suggestion in the prior art, generally similar, many of the bridge sections were provided with wheels, so that the entire bridge was moved by a tractor vehicle, after the sections had been assembled end to end, so that an extending end of the bridge made up of the connected sections would be pushed out over the depression, with the leading end eventually engaging the bank on the opposite side of the depression. In this construction, also, the bridge was constructed so as to have a length double that of the depression to be crossed, the additional sections of the bridge serving to counterbalance the sections extending over the depression. Thus, this prior art suggestion, also, required twice as many sections as was needed, could only span depressions of limited extent, and could not carry heavy loads.
The well known Bailey bridge, extensively used by the U.S. Army during World War II, while transportable, required a substantial crew to erect it and was limited in its load carrying capacity.
Other developments in the art of military bridging includes the scissors bridges, mounted on vehicles. These, too, could only be used to span depressions which were relatively narrow, and did not have great load carrying ability.